The capacity and coefficient of utilization of the positive active material of nickel-hydrogen cells show a significant increase when the cells are charged at −20°C or subjected to extended overcharge at 50°C. An interesting aspect of cells in which the positive plates show very high utilization is the appearance of a second wave in the overcharge region. The second wave seems to indicate the formation of a higher-valent nickel. The additional capacity obtained at very low temperature is less stable than that of 10°C when cycled. Destructive physical analysis of these cells reveals increased positive plate swelling. Rapid reaction of oxygen with hydrogen, otherwise known as popping, is more likely to occur in cells that contain positive plates which have endured significant swelling, since swelling occludes the gas channels.